So I went to fill up my 2010 Land Rover's LR2 A/C system and it showed a warning in red on the A/C canister before i even put in refrigerant. So I wore a glove and a pen and let the pressure down, then filled with 134a. I heard the compressor turn on, but no cold air at all. I filled till the gauge was in the green.
I then turned the temp dial to hot to check, and of course the air got hotter, so I don't think it's a stuck ventilation door? And I also replaced the air filter in the car with a new one before doing this.
I had the A/C on full and with recirculation turned on.
Just the fact that you describe the gauge as reading "red" and "green" tells us that you are not using a proper manifold gauge set, just the useless cheap gauge on a can of retail refrigerant. You need a full gauge set to diagnose AC systems. Hook one up and let us know what the system pressures are with the compressor running. Hopefully the can you used did not contain sealer!
